The disclosure relates generally to porous ceramic articles and more particularly to methods of forming porous ceramic articles using inert gas.
In the manufacture of porous ceramic articles, porosity and pore size distribution are generally achieved through the use of pore former ingredients, including organic materials, such as starches, and inorganic materials, such as graphite. These pore forming agents are burned off during firing to create voids or pores. However, the use of starches, graphite or a mixture of both can create severe complexities during both the drying and firing of ceramic bodies, especially relating to crack generation. For example, the depth of penetration of microwaves during drying of green bodies can be limited due to the presence of pore formers, such as graphite, or strong temperature gradients can occur in the green bodies during drying or firing. In addition, firing cycles may need to be tailored or lengthened to burn off pore formers, which can lead to higher costs, more complexity, and/or reduced production rates, particularly in the case of particulate filters where high porosity is required and, consequently, high levels of such pore formers are introduced. Exemplary particulate filters may be used for diesel engines (referred to as DPFs (diesel particulate filters)) and for gasoline engines (referred to as GPFs (gasoline particulate filters)).
Attempts to create high levels of porosity without use of excess amounts of starch or graphite pore formers have focused on, for example, the use of volatile hydrocarbons capable at volatilizing at a temperature below 200° C. or the use of carbon dioxide in a liquid state under very high pressure (e.g., at least 1650 psi). However, these approaches can have various drawbacks, including cost, environmental impact, extrusion stability issues, and non-uniform porosity.